The present invention relates to a dual stroke cylinder for stopping a piston in an intermediate position of a stroke and more specifically to a dual stroke cylinder for stopping a piston in an intermediate position of a stroke in a fluid pressure cylinder that is used for lifting such that a load is pushed up or pulled up by a rod of the piston or not for lifting such that the rod does not directly receive a weight of the load.
In a normal fluid pressure cylinder, a rod moves from a beginning to an end of a stroke at a single stroke. However, it is desired that the rod is once stopped in an intermediate position of the stroke with certain operation being done by that time and that the rod is then moved to the stroke end where operation in the next stage is done.
If the fluid pressure cylinder is controlled by a solenoid valve, energization of the solenoid valve may be interrupted by an unexpected accident. In such a case, a part of an operator""s body may be pinched by a workpiece or the like mounted to the rod at the beginning or end of the stroke of the rod. As a safeguard for preventing such a problem, it is more advantageous to use a fluid pressure cylinder in which a rod can stop in an intermediate position that is a non-energized home position than to use a lock mechanism or a three-position valve.
FIG. 8 shows an example of a known dual stroke cylinder in which a rod can stop in an intermediate position of a stroke. In the dual stroke cylinder, a first cylinder 1A having a first piston 2A with a stroke S1 and a first rod 3A and a second cylinder 1B having a second piston 2B with a stroke S2 that is larger than the stroke S1 and a second rod 3B are concentrically connected in series and a tip end of the first rod 3A airtightly passes through covers of the cylinders 1A and 1B to come in contact with the second piston 2B.
In this dual stroke cylinder, in a state shown in FIG. 8 in which the first and second pistons 2A and 2B and the first and second rods 3A and 3B are in return stroke end positions, if compressed air is supplied from a port 5A to a head-side cylinder chamber 7A of the first piston 2A, the first piston 2A and the first rod 3A move leftward in FIG. 8 by the stroke S1 and stop and the second piston 2B and the second rod 3B are pushed by the first rod 3A and move leftward by the stroke S1.
Then, if compressed air is supplied from a port 5B to a head-side cylinder chamber 7B of the second cylinder 1B, the second piston 2B and the second rod 3B further move leftward by a stroke (S2-S1) and stop.
Therefore, it is possible to stop the rod 3B of the second cylinder 1B in an intermediate position of the stroke S1.
If compressed air is supplied respectively from a port 6B to a rod-side cylinder chamber 8B of the second cylinder 1B and from a port 6A to a rod-side cylinder chamber 8A of the first cylinder 1A and compressed air in the head-side cylinder chambers 7A and 7B of the cylinders 1A and 1B is discharged to an outside, the second piston 2B and the second rod 3B move rightward by the stroke S2 and the first rod 3A and the first piston 2A move rightward by the stroke S1, thereby returning to the state shown in FIG. 8.
The port 6A on a rod side of the first cylinder 1A may be a breathing port.
Although the rod 3B can stop in the intermediate position of the stroke in the above dual stroke cylinder, the cylinder is formed by connecting the two cylinders 1A and 1B in series, which complicates the structure and increases the number of parts and cost. Moreover, it is necessary to control supply and discharge of compressed air to and from at least the respective ports 5A, 5B, and 6B of the two cylinders 1A and 1B and a structure of a system for controlling supply of the compressed air including pipe connection is complicated.
It is a main object of the present invention to provide a dual stroke cylinder in which a structure and a structure of a system for controlling supply of compressed air are simple, the number of parts is small, and cost can be reduced.
It is another object of the invention to provide a dual stroke cylinder in which a rod can stop not only in full-stroke positions but also in an intermediate stop position only by supply of compressed air to two ports.
To achieve the above objects, according to the invention, there is provided a dual stroke cylinder having a sleeve for intermediate stop and passing for sliding through a rod hole in a cylinder body, with a rod passing for sliding through the sleeve.
A base end portion of the sleeve is positioned in a rod-side pressure chamber and has a pressure receiving portion with a diameter smaller than that of the piston. The sleeve is stopped by stop means in the position when the sleeve moves to a forward end. Between the rod and the sleeve, first lock means for locking the rod and the sleeve to each other at a rearward end when the rod moves rearward relatively to the sleeve and second lock means for locking the rod and the sleeve to each other at a forward end when the rod moves forward relatively to the sleeve are provided.
According to a concrete embodiment of the invention, the stop means is a flange portion formed on an outer periphery of the base end portion of the sleeve and the flange portion is locked to an inner end of the rod hole in the cylinder body at the forward end.
According to another concrete embodiment of the invention, the first lock means is a large-diameter portion formed at the tip end of the rod, the large-diameter portion comes into contact with the tip end portion of the sleeve at the rearward end of the rod, the second lock means is the piston, and the piston comes into contact with a rear end portion of the sleeve at the forward end of the rod.
The dual stroke cylinder can be used for lifting such that a load is lifted or lowered by pushing the load up or by pulling the load up by the rod. The dual stroke cylinder can be used not for lifting such that the piston does not directly receive a weight of the load in the intermediate stop position.
If the cylinder is used as a lift for pushing up, pressure fluid of equal pressure is supplied to the head-side pressure chamber and the rod-side pressure chamber through the ports. If the cylinder is used as a lift for pulling up, pressure fluid of lower pressure is supplied to the head-side pressure chamber, pressure fluid of higher pressure is supplied to the rod-side pressure chamber, and a difference between the pressures of the fluid is maintained at such a value that the piston can stop in the intermediate stop position. If the cylinder is used not for lifting, the pressure fluid of lower pressure is supplied to the head-side pressure chamber, pressure fluid of higher pressure is supplied to the rod-side pressure chamber, and a difference between the pressures of the fluid is maintained at such a value that the piston can stop in the intermediate stop position.